Prior art of possible relevance includes the following U.S. Pat. No. 2,491,548 issued Dec. 20, 1949 to Branson; U.S. Pat. No. 2,736,212 issued Feb. 28, 1956 to Spence; U.S. Pat. No. 2,940,332 issued June 14, 1960 to Teague, Jr.; U.S. Pat. No. 3,050,258 issued Aug. 21, 1962 to Rauh; U.S. Pat. No. 3,103,829 issued Sept. 17, 1963 to Basford; U.S. Pat. No. 3,195,574 issued July 20, 1965 to Carls; U.S. Pat. No. 3,203,446 issued Aug. 31, 1965 to Smirra; U.S. Pat. No. 3,243,155 issued March 29, 1966 to Valente; U.S. Pat. No. 3,258,229 issued June 28, 1966 to Larson; U.S. Pat. No. 3,330,477 issued July 11, 1967 to Stephens; U.S. Pat. No. 3,839,923 issued Oct. 8, 1974 to Dean; U.S. Pat. No. 3,891,164 issued June 24, 1975 to Hertrick et al; and U.S. Pat. No. 3,981,466 issued Sept. 21, 1976 to Shah.
There exists a number of instances where the flow of fluid through a single valve is desirably controlled according to two or more differing schedules utilizing but a single control actuator for positioning a valve member with respect to a valve seat. For example, according to one schedule, a control input will result in a valve being moved from a full closed to a full open position. According to another schedule, the same input could provide valve movement from a full closed position to a partially open position.
One specific area in which such a system may find use is in turbine engines utilized in aircraft. Frequently, in such engines, so-called "bleed air" from the compressor section is taken from the engine prior to its admission to the combustion section for anti-icing purposes. The compressed air will be hot and thus may be advantageously employed to de-ice or prevent the formation of ice, at the air inlet to the engine and conceivably other locations on the aircraft as well.
At the same time, during the start-up of a turbine engine, it is desirable to "unload" the compressor section of the engine so as to allow a given rotational speed of the turbine to be achieved with minimal energy allowing the use of a smaller and lighter weight starter motor and to minimize start-up power requirements.
In both such instances, the function to be controlled is the flow of bleed air. However, the ultimate function to be provided, anti-icing or compressor section unloading, are quite different and thus have different requirements for bleed air. While two different systems, one for anti-icing bleed air and one for compressor section unloading bleed air could be provided, weight concerns are not served if this approach is adopted.
Thus, there is a real need for a simple multiple schedule valve that may be adapted readily to two different flow control schedules in response to essentially a single control input dictating position of a valve member with respect to a valve seat.